Low viscosity stable aqueous dispersion of graft carbon black

ABSTRACT

Aqueous dispersion of carbon black grafted with hydrophilic monomers such as alkali or ammonium carboxylate bearing polymers. The dispersion has a viscosity of about 2 to about 30 cP for a carbon black content of about 1-15% by weight.

The present invention relates to an aqueous suspension or dispersion ofcarbon black and, more especially to an aqueous suspension of carbonblack the particles of which are grafted with chemically bondedhydrosoluble polyolefinic chains, preferably polymers or copolymers ofacrylic monomers and, more particularly, ammonium and alkali metalpolyacrylates. In the present disclosure, the word "polyolefine"designates free radical polymerizable double-bonded monomers carryingwater solubilizing functions. Details on such monomers are providedhereafter.

The invention also concerns a method for preparing such an aqueoussuspension and the use thereof for manufacturing ink compositions,namely inks for jet-printing with jet-printing machines.

It is well known that jet-printing imposes certain difficultiesdepending upon the ink compositions to be used. For instance, such inksmust have a high optical density, i.e. contain a relatively highconcentration of carbon-black and simultaneously show a very lowviscosity and surface tension, i.e. of the order of 1.5 to 10 cP and 30to 50 dynes.cm, respectively. Also, the carbon-black particles ought tobe very fine so as to preferably pass freely through fine filters, e.g.1 to 50μ mesh filters. Further, in such suspensions, the carbon-blackparticles should not settle with time, i.e. they should remain insuspension for extended periods.

Carbon-black being essentially hydrophobic, attempts have been made toattain the above-mentioned properties by grafting water solublepolymeric radicals onto the carbon black particles thus making themwater compatible and freely dispersible in water.

Thus, in Japanese (opi) Patent Application No. 80,147561 (C.A. 94,192963) there is disclosed the grafting of carbon black particles withacrylic acid in ethanol in the presence of α,α'-azoisobutyronitrile(AIBN) and under irradiation. The thermal grafting and polymerization ofacrylate esters on carbon black is also disclosed in C.A. 94, 48453. InJapanese (opi) Application No. 74,81038, there is disclosed thepolymerization and grafting of styrene on carbon black in the presenceof AIBN at 140° C. (C.A. 82, 163002) and in Japanese Patent PublicationNo. 74,11557 (C.A. 81, 106311) there is disclosed the polymerization andgrafting on carbon black of acrylonitrile in the presence of AIBN inDMF. In DOS 2,130,617 (C.A. 76, 113947), there is described the directgrafting on carbon black of prepolymerized monomers and in JapanesePatent Publication No. 71,26970 as well as in GB-A-No. 1,191,872, thereis described the manufacture of carbon black with grafted acrylic acidand butyl acrylate copolymers in methyl-isobutylketone and other organicsolvents. Such grafted carbon black can be easily dispersed in aqueousammonia solutions.

In GB-A No. 1,421,529 there is disclosed the suspension polymerizationinto granules of olefinically unsaturated monomers in aqueous media inthe presence of carbon black and appropriate surfactants. Afterpolymerization, the formed polymer beads having the carbon blackincorporated therein are separated from the water phase and expanded.

The above techniques are effective but they either provide nohomogeneously dispersed hydrophilized carbon black particles or theyrely on the use of organic or aqueous-organic solvants for undertakingthe grafting of the carbon black particles. Yet, when such graftedparticles must be used in aqueous jet-ink formulations, the organicsolvents must first be removed and the particles must be redispersed inthe aqueous media suitable for such inks. Now, it has been found thatsuch a method is tedious and that the grafted particles do not dispersesufficiently well in the jet-ink formulations for providing compositionssuitable for being used in jet-printing machines.

Consequently, it was desirable that grafting and polymerization becarried out in water in such manner that a suitable aqueous dispersionor suspension of grafted carbon black be obtained which, afterwards, canbe directly converted into a jet-ink composition by the addition of theusual additional jet-ink components. It was further desirable thataqueous suspensions or dispersions of carbon black particles beobtained, the particles of which are rendered sufficiently hydrophilicto become highly water compatible and thus provide very low viscositysolutions even at high solid content. In such cases, the solubilizingpower of the groups grafted on the particles is so great thatdispersions very near to real solutions are involved. The aqueoussuspension of grafted carbon black of the invention has been obtained inthis manner. It is characterized by the following parameters: itsconcentration by weight of grafted carbon black is from about 1 to 15%and its viscosity is from about only 2 to 30 cP at room temperature. Theweight amount of water solubilizing grafted polymer or copolymer chainsis preferably from about 0.0001 to about 0.002 g (or 0.1 mg to 2 mg) persquare meter of the surface of the carbon black particles which isindeed an extremely small amount relative to the teaching of the priorart. Since the weight required of carbon black particles for making 1 m²varies from about 0.003 g to about 0.16 g, depending on the kind andgrade, the weight of grafted material per gram of carbon black will befrom about 0.0006 to 0.6 g; however, carbon blacks of grades rangingfrom 15 to 150 m² /g (i.e. 0.006 to 0.06 g/m²) are usually preferred.The number of monomer units linked together in the grafted chains ispreferably from about 20 to 200. The length of the grafted chains shouldbe sufficient to therefore provide adequate "solubility in water" (i.e.remarkably good dispersibility of the grafted particles) but not toogreat to avoid too large molecular weights with consequent too highviscosity and filterability problems. This also contrasts with the priorart where simultaneous grafting and polymerization to high polymersoccurs thus preventing the formation of "near solutions" of carbon blackin water like in the invention. With the above range of grafted chains,the present suspension filters rapidly through a 10μ mesh screen andslowly but acceptably through a 1μ mesh screen (for instance at a rateof 0.1 to 10 ml/min depending on pore size). It is believed that thepolyacrylate chains do crimp or coil at short distance from the carbonblack surface and pack over such surface with the carboxylate functionspointing radially toward the outside thus providing the right solubilityproperties, this being so when the pH is kept preferably between about 5and 9. Indeed, it has been shown that outside this pH range, the presentdispersion looses somewhat its desirable properties (e.g. sedimentationmay occur). It is particularly remarkable that hydrophobic carbon blackparticles can be made so well dispersible, i.e. nearly soluble, in waterwith grafted quantities of acrylate as low as about a tenth of amilligram per square meter of the carbon black. Naturally, theaforementioned parameters are not critically limiting and can exceed orfall short of the above mentioned ranges without departing from thescope of the invention.

The method of preparation of the aqueous dispersion of grafted carbonblack of the invention comprises treating carbon black in water with awater soluble peroxide and, after peroxidation, adding a water solubleacrylic monomer and a further amount of peroxide, whereby homogeneousfree radical polymerization of the monomer and grafting on the carbonblack particles will occur simultaneously. The reaction may be carriedout in the absence or in the presence of a free radical polymerizationaccelerator, for instance an amine accelerator.

Regarding mechanistic considerations pertaining to radical grafting oncarbon black, the following information can be provided.

Carbon black is essentially composed of carbon particles of generallyspherical shape bearing boundary oxygenated functions such ascarboxylic, phenolic and quinonic functions.

The phenolic and quinonic functions can act as polymerization quenchersas they will form, when reacting with initiators (for instance .sup.•CH₂ --CH₂ R), stabilized radicals (unreactive) viz. ##STR1##

In contrast, peroxides (for instance RCO--O--O--COR) will probablypredominantly react as follows: ##STR2##

The radicals formed in reaction ○3 will therefore promote olefinicpolymerization instead of inhibiting it as in reactions ○1 and ○2 .

The peroxides used in the present method are water soluble peroxidessuch as ammonium and alkali metal persalts, e.g. sodium, potassium andammonium persulfate and the corresponding perphosphates, perborates andthe like; alkali metal peroxides and hydrogen peroxide can also be used.Other peroxide initiators suitable in the present invention are listedin Encyclopedia of Polymer Science & Technology, vol. 2, IntersciencePublishers, p. 230-233, (1965).

The polymerizable olefinic monomers usable in the present method arepreferably the water soluble acrylic monomers such as the alkali metaland ammonium acrylates and methacrylates unsubstituted or substituted bywater solubilizing functions such as hydroxylic, ketonic and nitrilefunctions. Of course, alkali metals include sodium, potassium, lithiumand higher molecular weight alkali metals; ammonium includes the groupN⁺ H₄ and N⁺ R₄ in which R can be hydrogen or alkyl groups commonlyfound in current chemical practice. Substituted and unsubstitutedacrylic and methacrylic acid compounds with unsalted free carboxylicgroups are also usable but less preferred as the viscosities of theresulting graft carbon black aqueous dispersions thus obtained are notas low as when using the monomers in the alkali salt form. Furthermore,it was found that when treating such free COOH containing graft carbonblack aqueous dispersions with alkali metal hydroxide in view ofobtaining dispersions identical with that obtained directly with thealkali salt monomers, viscosities increased quite unexpectedly insteadof decreasing. In addition, other water soluble vinyl monomers such asacrylamide, methacrylamide, N-vinyl-pyrrolidone and hydroxyethyl acrylicacid are also possible preferably in admixture with the aforementionedacrylates. Some further monomers usable in this invention are listed inthe aforementioned Encyclopedia of Polymer Science & Technologyreference.

The carbon black can be selected from various sources and include theusual types of carbon black, namely channel black, thermal black, lampblack and furnace black. Furnace black is preferred. Reference showingcarbon usable in this invention are: DONNET and VOET: Carbon BlackPhysics, Chemistry and Elastomer Reinforcement, Marcel Dekker Inc.,(1976).

If accelerators are used in the present method, commonly available freeradical polymerization accelerators can be used; amine accelerators areconvenient such as tetramethyl ethylenediamine, pentamethyl diethylenetetramine, hexamethyl triethylene pentamine and the like.

For carrying out the present simultaneous polymerization and grafting ofcarbon black with olefinic monomers, it is preferable to agitate theingredients in water at a temperature of 50° C. to 100° C., preferablyat reflux temperature. The reaction time is from about 1 hr to about 60hrs at reflux temperature although longer reaction times are not harmfulbut not economical. After cooling, the ungrafted homopolymer which isproduced as a by product can be removed by usual techniques, e.g. freezedrying, centrifugation or dialysis but, for most uses, this is notnecessary, the presence of such homopolymers not being detrimental forfurther uses of the grafted carbon black dispersion in jet-inkcompositions. On the contrary, the presence of the homopolymers in thesolution will serve as a binder ingredient useful for improving theadhesion of the ink on the printed surfaces and the cohesion of thecarbon black particles together. This factor was unexpected andsurprising and provides a considerable advantage to the dispersion ofthe invention over the prior art compositions in jet-ink applications.

The quantities of reagents to be used in the method of the invention areas follows: in the first peroxidation stage, there can be used for 100 gof carbon black from about 10 to 50 g of peroxide counted as K₂ S₂ O₈ ormole-equivalents of other water soluble peroxides and, when an amineaccelerator is used, about 0.1 to 5 g of such an amine, e.g.N-tetramethyl ethylenediamine (TEMED) or mole-equivalent quantities ofother amine accelerators. These quantities are however not criticalprovided enough peroxidant is used. The peroxidation can be carried outat 50°-100° C. under stirring in water for about 1 to 24 hrs but theseconditions are not critical provided that the reaction is allowed to goto completion.

In the second stage, i.e. the grafting stage, the quantities of olefinicmonomers that can be used can vary from approximately 0.01mole-equivalent to about 0.5 mole-equivalent per gram of carbon black.The quantities of monomers to be used are obviously related to thedensity of grafting sites on the carbon black particles that variesconsiderably from one type of carbon black to the other and is generallyrelated to the quinone and phenol function area density on theparticles. According to the data of the main manufacturers of carbonblack, such quinone and phenol group densities can vary from about 1 toabout 3000 μequiv./g of carbon black which, in view of the aforegivenrange of area per gram values (depending on the kind of carbon black)will provide figures ranging from about 0.01 μequiv./m² to about 10μequiv./m². Thus, the amount of monomer in the grafting stage will beadapted as a function of the grafting equivalence selected and thegrafting site density of the carbon black used.

The amount of peroxide to be used in the polymerization grafting stagesdepends on the amount of monomer used and can be comprised from about0.01 g to 0.1 g (counted as K₂ S₂ O₈) per gram of the monomer.Equivalents of other peroxides are also usable. When using also an amineaccelerator, for instance TEMED or equivalents of other amineaccelerators, quantities of the order of 0.01 to 1 g of TEMED per gramof peroxide (counted as K₂ S₂ O₈) are advantageously usable. All theabove reagent ratios and quantities are not critical and can fall shortof or exceed the given limits in some cases, provided of course, thatthe amounts of respective reagents are enough for accomplishing thereactions and not in such excess as becoming non economical.

The aqueous suspension of grafted carbon black of this invention isdirectly usable for making jet-ink compositions. For this, it issufficient to add to the suspension the suitable amounts of usualjet-ink additives, such as wetting agents, surfactants and viscositycontrolling agents, dyes, mold inhibitors, oxygen absorbers, bufferingagents, pH controlling agents. In the present invention, a considerableand unexpected advantage is provided by the presence of the residualhomopolymer which was formed during polymerization and grafting. Assurfactant products, non ionic compounds such as polyoxyethylenesorbitan monolaurate and the like are preferred. As wetting agents,polyglycols or glycolamines such as diethylene glycol, glycerine,α-thiodiglycol, triethanolamine and N,N-dimethoxy-methyl-2-imidazolidoneare suitable. The quantities of such additives will conform to usualpractice.

As dyes, CI acid black Nos. 1, 24, 26, 48, 58, 60, 109, 119 and 131 canbe used. As mold inhibitors, sodium dehydroacetate,1,2-benzisothiazolin-3-one, 6-acetoxy-2,4-dimethyl-m-dioxane orformaldehyde can be used. As oxygen absorbers, sodium sulfite, sodiumbisulfite can be used. As pH controlling agents, HCl and NaOH can beused.

In addition to the aforementioned use in jet-printing inks, the aqueousdispersion of the invention can be used for many other purposes. Amongsuch purposes, one may recite inks for fountainpen, ballpoint pen, feltpen, intaglio, rotogravure, rotary printing, elastographic printing,typographic printing, rotary news-paper and the like.

The following Examples illustrate the invention.

EXAMPLE 1 (Comparative)

Forty three grams of carbon black (grade "Regal-R", quinone density 2μequi./g, CABOT Corp.) were agitated with 300 ml of water and 30 ml ofethanol. Then, 4.3 g of ammonium persulfate and 0.2 g ofN-tetraethyl-ethylenediamine (TEMED) were added and the mixture wasstirred for 18 hrs at 90° C. Then, 43.2 g of acrylic acid and 1 g of(NH₄)₂ S₂ O₈ were added and the mixture was stirred under reflux at95°-98° C. for 24 hrs. After cooling, there was obtained a welldispersed suspension of polyacrylic grafted carbon black the solidconcentration of which was about 14%. The pH of this solution was about2 and its viscosity about 45 cP. Dilution with about 200 ml of waterprovided carbon black dispersion of good opacity and much lowerviscosity usable as a printing jet-ink. Upon neutralization with diluteNaOH solution, the viscosity increased.

EXAMPLE 2

Fifteen grams of carbon black (grade "Regal R") in 50 ml of H₂ O wereagitated for 4 hrs at 95° C. with 1.5 g of (NH₄)₂ S₂ O₈ and 0.1 ml ofTEMED after which a solution of 22.5 g of acrylic acid in 41.6 ml of 30%aqueous NaOH solution was added with 2 g of (NH₄)₂ S₂ O₈ and 0.1 ml ofTEMED. The mixture was further agitated for 24 hrs at 95° C. Then it wascooled and provided a dispersion (E) of about 20% solid grafted carbonblack. The pH was 5.7 and the viscosity 7.1 cP. Lower viscosities withstill acceptable opacity (blackness) were obtained by dilution toapproximately 10-15% dispersed solids.

The experiment was repeated as described but using 0.3 ml of TRIS-TEMED(TRIS means tris-(hydroxymethyl)-aminomethane) instead of the TEMED inthe peroxidation stage and no amine in the polymerization graftingstage. A dispersion (F) of comparable solid concentration was obtainedwith viscosity 4.9 cP and pH 5.5. It however settled after 3 minsedimentation by centrifugation under 3300 rpm and was consideredunacceptable.

Dispersions (G and H) of corresponding concentrations were made exactlyas disclosed for dispersions E and F, respectively, but replacing the"Regal-R" carbon black by type "Elftex-5" (Furnace black) carbon black.Dispersion G had a pH of 5.7 and a viscosity in undiluted form of 12.1cP; it did not settle after 30 min centrifugation. Dispersion H had a pHof 5.4 and a viscosity of 7.1 cP in undiluted form. It settled after 24min centrifugation. There was no substantial precipitation after 1 yearstorage at room temperature.

EXAMPLE 3

The experiment of Example 2 was repeated four times (samples I1-I4)using 100 g of water, 15 g of carbon black ("Elftex-5") 1.5 g of K₂ S₂O₈, 0.3 ml of TEMED and a temperature of 95° C. in the peroxidationstage, and 22.5 g of acrylic acid, 65 ml of 30% NaOH, 2 g of K₂ S₂ O₈, 1ml of TEMED, and 35-40 hrs boiling temperature (98° C.) in thepolymerization grafting stage. The variable was the peroxidationduration which was 1 hr (I1), 2 hrs (I2), 4 hrs (I3) and 6 hrs (I4). Nosignificant differences between the results were found, all dispersionshaving a pH of 5.8-6.0 and viscosities of about 15-17 cP in undilutedform. Much lower viscosities, with still acceptable opacities, werefound with dispersions diluted down to about 5-10% grafted solids.

EXAMPLE 4

The experiments of Example 2 were repeated under the followingconditions:

Peroxidation stage: water 100 ml; carbon black ("Elftex-5") 15 g; K₂ S₂O₈ and TEMED variable according to Table I below; 2 hrs at 95° C.

Grafting and polymerization stage: sodium acrylate from 22.5 g acrylicacid neutralized with 65 ml 30% NaOH; K₂ S₂ O₈ 2 g; TEMED 1 ml; 24 hrsat 98° C. Four samples (J1 to J4) were prepared according to the furtherdata in Table I below and gave corresponding dispersions withviscosities also given in the Table.

                  TABLE I                                                         ______________________________________                                        Samples  K.sub.2 S.sub.2 O.sub.8 (g)                                                               TEMED (ml)  Viscosity (cP)                               ______________________________________                                        J1       1.5         0.15        13.6                                         J2       2.25        0.23        18.7                                         J3       3.0         0.30        15.3                                         J4       3.75        0.38        18.0                                         ______________________________________                                    

Upon dilution with water to provide 5-10% solid low viscosity aqueousdispersions, the above samples still had acceptable opacities andsettling times.

EXAMPLE 5

Experiments (K1 to K4) similar to those reported in Example 4 wereperformed under the following conditions, except for the K₂ S₂ O₈ andTEMED used in the second stage which were as indicated in the next TableII.

Peroxidation stage: water 100 ml; carbon black ("Elftex-5") 15 g; K₂ S₂O₈ 3 g; TEMED 0.3 ml; 2 hrs at 95° C.

Grafting and polymerization stage: Na acrylate from 22.5 g of acrylicacid neutralized with 65 ml of 30% NaOH solution; K₂ S₂ O₈ and TEMED seeTable II; 48 hrs at 98° C. The remaining data and results are recordedin the next Table.

                  TABLE II                                                        ______________________________________                                        Samples  K.sub.2 S.sub.2 O.sub.8 (g)                                                               TEMED (ml)  Viscosity (cP)                               ______________________________________                                        K1       1.0         0.5         10.4                                         K2       1.5         0.75        17.7                                         K3       2.0         1.0         19.6                                         K4       2.5         1.25        16.6                                         ______________________________________                                    

Upon centrifugation at 3300 rpm, the settling time for all samples wasover 3.5 hrs.

EXAMPLE 6

Experiments like in the previous Examples (samples L1 to L4) werecarried out with variable amounts of acrylic monomer, K₂ S₂ O₈ and TEMEDin the polymerization grafting stage (see Table III below).

Moreover, the following conditions were used:

Peroxidation stage: water 100 ml; carbon black ("Elftex-5") 15 g; K₂ S₂O₈ 3 g; TEMED 0.3 g; 2 hrs at 95° C.

Grafting & Polymerization stage: acrylic acid, K₂ S₂ O₈ and TEMEDaccording to Table below; 46 hrs at 98° C.; neutralization NaOH 65 ml ofaqueous solution containing required NaOH neutralizing equivalent. Thesedimentation time after centrifugation at 3300 rpm is also shown inTable III.

                  TABLE III                                                       ______________________________________                                                                        Vis-  Centrifuga-                                    Acrylic  K.sub.2 S.sub.2 O.sub.8                                                                TEMED  cosity                                                                              tion settling                           Samples                                                                              (g)      (g)      (ml)   (cP)  (min)                                   ______________________________________                                        L1     10       0.88     0.44   6.6    30                                     L2     15       1.33     0.67   5.7    30                                     L3     22.5     2        1.0    13.7  >90                                     L4     30       2.66     1.33   27.1  >90                                     ______________________________________                                    

The grafting level for samples L1 and L2 was considered borderline toachieve optimal conditions of opacity and viscosities. (for opacitymeasurements, see for instance Example 9)

EXAMPLE 7

The importance of using carbon black types with a high density ofgrafting sites was evidenced by repeating the experiments of theprevious examples with other grades of carbon black, i.e. "Regal-R" (2μequiv. of quinone sites/g) and "Vulcan 6" (70 μequiv. of graftingsites/g). Pertinent data on both the peroxidation and grafting stagesare outlined below in Tables IV and V. In the Tables a previous sample(L3 from Example 6) is included for comparison. Except for the specificdata reported in the Tables, the other conditions were as disclosed inExample 5.

                  TABLE IV                                                        ______________________________________                                        (peroxidation)                                                                       Carbon black   Quinone                                                 Sample type and quantity                                                                            conc.    specific surface                               (no)   (g)            (μeg./g)                                                                            (m.sup.2 /g)                                   ______________________________________                                        L3     Elftex-5 (15)  18        74                                            L5     Regal-R (13.9)  2        80                                            L6     Vulcan-6 (9.7) 70       115                                            M3     Vulcan-6 (15)  70       115                                            ______________________________________                                    

                  TABLE V                                                         ______________________________________                                        (Polymerization & Grafting)                                                                         Centrifugation                                          Sample Viscosity of grafted                                                                         settling at  Optical                                    (No)   solution (cP)  3300 rpm (hrs)                                                                             density                                    ______________________________________                                        L3     13.7           >2.5         1.40-1.45                                  L5      6.3           <0.5         0.96-0.98                                  L6      6.7           >2.5         1.15-1.22                                  M3     18.8           >2.5         1.44-1.48                                  ______________________________________                                    

The data of Table V show that using carbon black with high specificsurfaces provides more favorable combinations of high optical densityand low dispersion viscosity.

EXAMPLE 8

A sample of grafted carbon black was prepared under the same conditionspertaining to sample L6 in Example 7 but varying the grafting andpolymerization duration. The other general reaction parameters arelisted below:

Peroxidation stage: water 100 g; carbon black ("Elftex-5") 15 g; K₂ S₂O₈ 3 g; TEMED 0.3 ml; 2 hrs at 95° C.

Grafting & Polymerization: acrylic acid 22.5 g; neutralization 30% NaOH65 ml; K₂ S₂ O₈ 2 g; TEMED 1 ml; temperature 98° C.; duration see below.

    ______________________________________                                        Grafting and polymerization                                                                     Viscosity of suspension                                     duration (hrs)    (cP)                                                        ______________________________________                                         0                not measured                                                 5                12.2                                                        21                13.3                                                        45                13.4                                                        69                17.5                                                        91                18.8                                                        ______________________________________                                    

From the above data, it can be seen that acceptable viscosities (i.e.degree of grafting) are obtained after about 5 hrs reaction time.Reaction periods over about 60-70 hrs will unduly raise the viscositywithout much improvement to the grafting yield.

EXAMPLE 9

A sample of aqueous dispersion of grafted carbon black ("Elftex-5)"similar to sample L3 (see Example 6) was diluted with water until itscontent in grafted carbon black was approximately 5-15% by weight. Thenvarious preparations of such sample were mixed with usual jet-printingink ingredients according to Table VI below. The viscosity, opticaldensity and surface tension parameters were measured and are alsogathered in Table VI. All solutions passed quickly through a 10μ meshfilter and slowly (but still acceptably) through a 1μ mesh filter.Optical densities above about 0.80 are considered acceptable for ajet-print ink.

Opacities were measured as follows: about 0.5 to 1 g of the inkcomposition was placed on a piece of jet-print paper and spread to alayer of 15μ with a suitably calibrated doctor's blade. The film wasallowed to dry in air at room temperature for about 30 sec and theopacity was measured according to usual standards with a McBethdensitometer.

                  TABLE VI                                                        ______________________________________                                        Sample of ink    L32     L31       L305                                       ______________________________________                                        Solution (ml)    103     51.5      77.25                                      Ethylene glycol (g)                                                                             8       4         2.75                                      Water (ml)       --      --        25                                         10% aqueous glycol (ml)                                                                        --      55.5      --                                         Tween 20 (10% aqueous poly-                                                                    16      10        15                                         alkylene sorbitan monolaurate)                                                Viscosity (cP at 21° C.)                                                                7.5      5.1      6.0                                        Surface tension (dyne/cm)                                                                      38      37        38                                         Optical density (15/u wet                                                                      1.45    0.86-0.94 1.08-1.12                                  ink film)                                                                     ______________________________________                                    

We claim:
 1. A stable aqueous dispersion or suspension of carbon blackthe particles of which are grafted with chemically bonded water solublepolyolefinic chain residues selected from alkali metal and ammoniumpolyacrylates the dispersed carbon black solid content of which is fromabout 5 to 15% by weight and the viscosity is from about 2 to 30 cP atroom temperature.
 2. The dispersion of claim 1, in which the pH is 5 to9.
 3. The dispersion of claim 2 which has an optical density of 0.8 to1.5 as measured on a dry film obtained from a 15μ wet film of dispersionwith 5-15% by weight of grafted carbon black.
 4. The dispersion of claim2, wherein the quantity of water solubilizing grafted polymer orcopolymer chain residues is from about 0.1 to 2 mg by square meter ofthe carbon black particles area.
 5. The dispersion of claim 2, whereinthe average number of monomer units polymerized together in the graftedchain residues is from about 20 to
 200. 6. The dispersion of claim 2,having a filterability though a 10μ mesh screen of 1-30 ml/min andthough a 1μ mesh screen of 0.1-10 ml/min.
 7. The dispersion of claim 2,wherein the carbon black is selected from thermal black, lamp black,channel black and furnace black.
 8. The dispersion of claim 2, whichcontains in addition from 0.1 to 20% by weight of ungrafted homo- orcopolymer the latter acting as a binder.
 9. A method for the preparationof the suspension of claim 1, comprising (1) heating carbon black inwater with a peroxide under agitation until the quinone and phenolradical quencher functions at the surface of the carbon particles havebeen inhibited and converted into grafting sites, then (2) adding atleast one suitable radical polymerizable water solubilizing monomer,selected from the group consisting of alkali metal and ammoniumacrylates and effecting a simultaneous polymerization and grafting ofsaid monomer on the carbon black particles in the presence of awater-soluble peroxide radical polymerization initiator.
 10. The methodof claim 9, wherein there is used, in addition to the water-solubleperoxide, a radical polymerization amine accelerator.
 11. The method ofclaim 10, wherein the amine accelerator is selected fromN,N-tetraalkyl-ethylenediamine andN,N',N"-pentaalkyl-diethylenetriamine.
 12. The method of claim 9,wherein the water-soluble peroxide is selected from ammonium and alkalimetal persulfates, perborates, perphosphates, and alkali metalperoxides.
 13. The method of claim 12, wherein the water-solubleperoxide is (NH₄)₂ S₂ O₈, K₂ S₂ O₈ or Na₂ S₂ O₈.
 14. The method of claim9, wherein the weight ratio of water-soluble peroxide to carbon black inthe peroxidation stage (1) is about 0.1 to 0.5.
 15. The method of claim9, wherein the average density of the grafting sites on the selectedcarbon black before peroxidation is from about 1 to 3000μ equivalentsper gram of particles.
 16. The method of claim 15, wherein the weightratio of polymerizable monomer to carbon black is approximately 0.5 to30.
 17. The method of claim 16, wherein the amount of water-solubleperoxide in stage (2) is about 0.01 g to 0.1 g per gram of monomer. 18.The method of claim 12, wherein the amount of amine initiator is about0.01 to 1 g per gram of peroxide.
 19. The method of claim 9, wherein thetemperature of steps (1) and (2) is from about 50° to 100° C. underordinary pressure.
 20. The method of claim 9, wherein the duration ofstep (2) is approximately 1 to 60 hrs.
 21. A method for making jet-inkformulations, comprising the step of adding to said dispersion, definedin claim 1 wetting agents, surfactants, viscosity controlling agents,dyes, mold inhibitors, oxygen absorbers, or pH controlling agents.
 22. Amethod for making jet-ink formulations comprising the step of adding tosaid dispersion defined in claim 8 wetting agents, surfactants,viscosity-controlling agents, dyes, mold inhibitors, oxygen absorbers,or pH-controlling agents, the residual ungrafted homopolymers presentacting as an adhesive for the ink on the printed surface and as acohesive agent for the carbon black particles.